Increasing the oxidation resistance of molybdenum and its use for lamp seals

Abstract

The life of electric lamps exposed to an oxidizing environment at elevated temperature and having hermetic seals between molybdenum and a vitreous material is substantially increased by applying alkali metal silicate to the surface of that portion of the molybdenum in the seal area which is exposed to said oxidizing environment.

What is claimed is: 
     
       1. A seal between molybdenum and a vitreous material having improved life when exposed to an oxidizing environment at elevated temperatures of at least about 250° C. wherein that portion of said molybdenum of said seal which is exposed to said oxidizing environment has been coated with an aqueous solution of alkali metal silicate. 
     
     
       2. The seal of claim 1 wherein that portion of said molybdenum exposed to said oxidizing environment contains a relatively uniform coating of said alkali metal silicate. 
     
     
       3. The seal of claim 2 being a hermetic seal. 
     
     
       4. The seal of claim 3 wherein said vitreous material is quartz or high temperatures glass. 
     
     
       5. The seal of claim 4 wherein said elevated temperature does not exceed about 600° C. 
     
     
       6. The seal of claim 5 wherein said alkali metal comprises potassium. 
     
     
       7. The seal of claim 5 wherein said alkali metal comprises sodium. 
     
     
       8. The seal of claim 5 wherein said alkali metal is selected from the group consisting essentially of potassium, sodium or mixture thereof. 
     
     
       9. An electric lamp comprising a vitreous envelope having at least one metal inlead construction hermetically sealed in at least one end thereof and extending into said end through at least one opening extending into said envelope wherein said inlead construction comprises an outer metal lead, an intermediate molybdenum sealing foil which forms said hermetic seal with said vitreous envelope and an inner lead extending into said envelope, said inner and outer leads being connected to said sealing foil, wherein the surface portion of said sealing foil which is adjacent said outer terminal lead is exposed to an oxidizing environment and has been coated with an aqueous solution of alkali metal silicate. 
     
     
       10. The lamp of claim 9 wherein said vitreous envelope is quartz or aluminosilicate glass. 
     
     
       11. A lamp according to claim 10 comprising a tungsten halogen lamp or an arc discharge lamp. 
     
     
       12. A lamp according to claim 11 wherein said inner and outer metal leads comprise refractory metal. 
     
     
       13. A lamp according to claim 12 wherein said outer lead is coated with a metal which does not adhere to said lamp envelope. 
     
     
       14. An electric lamp comprising a vitreous envelope having at least one refractory metal inlead construction pinch-sealed into at least one end thereof and extending into said through at least one opening extending into said envelope wherein said inlead construction comprises an outer terminal lead, an intermediate molybdenum sealing foil which forms a hermetic seal with said quartz envelope and an inner lead extending into said envelope, said inner and outer leads being connected to opposite ends of said sealing foil and wherein the surface of that portion of said molybdenum sealing foil adjacent said outer terminal lead is exposed to an oxidizing environment and has been coated with an aqueous solution of alkali metal silicate. 
     
     
       15. The lamp of claim 13 wherein said seal is a hermetic seal. 
     
     
       16. The lamp of claim 15 wherein said vitreous envelope comprises quartz or a high temperature glass composition. 
     
     
       17. A tungsten-halogen lamp according to claim 16. 
     
     
       18. The lamp of claim 17 wherein said envelope consists essentially of quartz. 
     
     
       19. An arc discharge lamp according to claim 18. 
     
     
       20. The lamp of claim 18 wherein said alkali metal comprises potassium. 
     
     
       21. The lamp of claim 18 wherein said alkali metal comprises sodium. 
     
     
       22. The lamp of claim 18 wherein said alkali metal consists essentially of potassium. 
     
     
       23. A reflector and lamp combination comprising (i) a vitreous reflector member having a front reflecting portion terminating in an elongated hollow cavity portion which protrudes rearwardly from said reflector member and (ii) a tungsten-halogen lamp permanently secured in said hollow cavity portion with a cement so that its light source is positioned at about the focal point of said reflector-member said tungsten-halogen lamp comprising a vitreous envelope having at least one refractory metal inlead construction hermetically sealed into at least one end thereof and extending into said end through an opening extending into said envelope wherein said inlead construction comprises an outer terminal lead, an intermediate molybdenum sealing foil which forms said hermetic seal with said vitreous envelope and an inner lead extending into said envelope, said inner and outer leads being connected to opposite ends of said sealing foil and wherein the surface of that portion of said molybdenum foil adjacent said outer terminal lead is exposed to an oxidizing environment and has been coated with an aqueous solution of alkali metal silicate. 
     
     
       24. The construction of claim 23 wherein said outer lead is coated with a mineral which does not adhere to said vitreous envelope. 
     
     
       25. The construction of claim 24 wherein said outer lead has a diameter of at least about 40 mils. 
     
     
       26. Molybdenum having improved resistance to oxidation at temperature between about 250°-600° C. the surface of which has been coated with an aqueous solution of alkali metal silicate which has been dried prior to exposure of said molybdenum to said temperature. 
     
     
       27. A process for improving the oxidation resistance of molybdenum at temperatures between about 250°-600° C. which comprises applying an aqueous solution of alkali metal silicate to the surface thereof and then drying said solution to form a coating of alkali metal silicate on said surface. 
     
     
       28. The construction of claim 24 wherein said alkali metal is selected from the group consisting essentially of potassium, sodium or mixture thereof. 
     
     
       29. The construction of claim 28 wherein said alkali metal consists essentially of potassium. 
     
     
       30. The molybdenum of claim 26 wherein said alkali metal is selected from the group consisting essentially of potassium, sodium or mixture thereof. 
     
     
       31. The molybdenum of claim 30 wherein said alkali metal consists essentially of potassium. 
     
     
       32. The process of claim 27 wherein said alkali metal is selected from the group consisting essentially of potassium, sodium or mixture thereof. 
     
     
       33. The process of claim 32 wherein said alkali metal consists essentially of potassium. 
     
     
       34. The lamp of claim 16 wherein said outer leads are coated with a metal which does not adhere to said lamp envelope. 
     
     
       35. The lamp of claim 34 wherein said alkali metal silicate consists essentially of potassium silicate, sodium silicate or mixture thereof.